The quick ash from a coal-operated power plant boiler contains a plurality of components, the main part thereof constituted by SiO.sub.2, Al.sub.2 O.sub.3, Fe.sub.2 O.sub.3, CaO, MgO, and combustible substances. The content of combustible substances, that is mainly coal, in the quick ash may vary within wide limits (0.5 to 20%), depending e.g. on the coal quality, on the condition of the grinders used in comminuting the coal and the adjustment of burners, on the design of the boiler, and on the amount of combustion air. It may be said in general that the quantity of unburned fuel in the quick ash tells about how incompletely/completely the combustion in the boiler takes place. The coal losses, that is the coal that is lost along with the ash, may involve even quite spectacular costs. For instance, in a 500 megawatt power plant (running period 6000 hrs per annum, consumption ratio 2.6, coal price U.S. $60 per ton) the annual expenditures for fuel are about $60 million; and a 1% coal loss, which is equivalent to about 10% coal content in the quick ash, amounts to $0.6 mill. at annual level.
Furthermore, it is substantially important to monitor the coal content of quick ash also in view of the useful applications to which the ash may be put. Quick ash with excessively high coal content is not usable for instance in light-weight gravel production, nor as a constituent in mortar, in cement, etc. In addition, the variation of this coal content restricts the use of quick ash in brick production, as a raw material for autoclaved products, etc.
It is present practice to analyze the quick ash of coal-operated power plants in service laboratories, by analytical methods. The results are usually not obtained until several hours after sampling. It is therefore hardly possible to use the numerical values of the coal losses thus obtained as any kind of guiding values in the control of the combustion process, nor to the purpose of adjusting the coal losses to be at desired level.
The object of the present invention is to eliminate the drawbacks mentioned. A particular object of the invention is to provide a procedure and apparatus for measuring the coal content of quick ash, continuously or periodically, so that the measured values may be employed in process control to regulate the coal losses to be at a desired level, and towards supervision of the combustion means functioning and towards quality control of the ash produced in the combustion, for instance of ash that is meant to be sold.
Regarding the features which are characteristic of the invention, reference is made to the claims section.